600mpa grade al-zn-mg-cu alloy and method for manufacturing sheet therefrom

Abstract

This invention relates to the field of non-ferrous metal processing technology, specifically to a 600MPa grade Al-Zn-Mg-Cu alloy and its sheet preparation method. The 600MPa grade Al-Zn-Mg-Cu alloy comprises 7.4–8.5 wt.% Zn, 1.4–2.0 wt.% Mg, 2.0–2.4 wt.% Cu, Zr, Sc, and impurities, with a total Zr and Sc content of 0.04–0.12 wt.% and a total impurity content ≤0.04 wt.%. The Cu / Mg mass percentage ratio is ≥1.2, and the Zn / Mg mass percentage ratio is 4.5–5.1. The purpose of this 600MPa grade Al-Zn-Mg-Cu alloy and its sheet preparation method is to solve the problem of simultaneously meeting the requirements for strength, toughness, and corrosion resistance in aluminum alloys.

Description

Technical Field

[0001] This invention relates to the field of non-ferrous metal processing technology, specifically to a 600MPa grade Al-Zn-Mg-Cu alloy and its plate preparation method. Background Technology

[0002] Structural weight reduction is a perpetual theme and pursuit in aerospace structural design, which always pushes materials to their limits. In the weight reduction of second- to fourth-generation fighter jets, 70% of the contribution comes from materials technology. Selecting advanced materials with high specific strength, high specific stiffness, and high damage tolerance is one of the main measures to reduce structural weight and lower the structural weight coefficient. Aluminum alloys are the main material for aircraft airframe structures, accounting for about 60% in third-generation aircraft structures and still more than 40% in fourth-generation aircraft. Currently, the most widely used aluminum alloy is 7050-T7451. Taking plates with a thickness of 76-102mm as an example, its tensile strength is ≥496MPa, with actual usage values ​​slightly exceeding 500MPa. The newly developed 7085 aluminum alloy in recent years can reach a strength of 550MPa, an improvement of about 10% over 7050-T7451, but it still cannot meet the urgent needs of increasingly sophisticated aerospace structural optimization. Currently, there is an urgent need for 600MPa-grade aluminum alloy materials.

[0003] Furthermore, the strength of aluminum alloys exhibits a contradictory trend with their toughness and corrosion resistance; increased strength leads to a significant decrease in both. Currently, engineered sheet metal of alloys such as 7055 and 7056 can achieve a strength of 600 MPa, but their overall performance does not meet design requirements. Taking 7055 aluminum alloy as an example, its tensile strength can exceed 600 MPa, but its fracture toughness is more than 40% lower than that of 7050-T7451 aluminum alloy, and its corrosion resistance is at least one level lower, significantly reducing its service life. Moreover, 7055 has poor hardenability; with increasing thickness, its strength decreases considerably, and there is a risk of quenching cracks. Currently, the maximum thickness allowed by international standards is only 38 mm.

[0004] To improve the strength of an alloy, one approach is to increase the element content and the number of precipitates, such as in 7056 and 7055 aluminum alloys. However, high-zinc, high-magnesium, and high-copper content ingots of ultra-strong aluminum alloys are prone to cracking and exhibit significant microstructural inhomogeneity, making the actual production of thick plates ≥80mm extremely difficult. Another approach is to employ a lower aging process to prevent excessively coarse precipitate growth and fully utilize the strengthening effect of the precipitates. For example, the tensile strength of 7150-T7651 thick plates is generally between 585 and 605 MPa. However, due to its lower alloy element content, such as an average Zn content of 6.2%, significantly lower than the 9% of 7056, its strength cannot be consistently guaranteed above 600 MPa. Furthermore, the T76 aged state exhibits lower exfoliation corrosion resistance, failing to meet the requirements for high corrosion resistance.

[0005] Therefore, the inventors provide a method for preparing a 600MPa grade Al-Zn-Mg-Cu alloy and its sheet. Summary of the Invention

[0006] (1) Technical problems to be solved

[0007] This invention provides a 600MPa grade Al-Zn-Mg-Cu alloy and its plate preparation method, which solves the technical problem that aluminum alloys are difficult to simultaneously meet the requirements for strength, toughness and corrosion resistance.

[0008] (2) Technical solution

[0009] This invention provides a 600MPa grade Al-Zn-Mg-Cu alloy, comprising 7.4–8.5 wt.% Zn, 1.4–2.0 wt.% Mg, 2.0–2.4 wt.% Cu, Zr, Sc, and impurities by mass percentage, wherein the total content of Zr and Sc is 0.04–0.12 wt.% and the total content of the impurities is ≤0.04 wt.%; wherein the Cu / Mg mass percentage ratio is ≥1.2 and the Zn / Mg mass percentage ratio is 4.5–5.1.

[0010] Furthermore, when the Sc content is >0.02 wt.%, the total content of Zr and Sc is less than 0.08 wt.%; when the Sc content is <0.01 wt.%, the total content of Zr and Sc is greater than 0.08 wt.%.

[0011] Furthermore, the impurities contain Cr content ≤0.01 wt.%, Mn content ≤0.01 wt.%, Si content ≤0.02 wt.%, and Fe content ≤0.02 wt.%.

[0012] This invention also provides a method for preparing 600MPa grade Al-Zn-Mg-Cu alloy plates, comprising the following steps:

[0013] High-purity electrolytic copper, Al-Zr5 master alloy, industrial pure zinc, and high-purity magnesium are added to the smelted pure aluminum, mixed evenly, and then refined multiple times. After filtration and slag removal, the mixture is cast into ingots.

[0014] The ingot is subjected to multi-stage homogenization treatment and multi-pass rolling to obtain rolled sheet material;

[0015] The rolled sheet is subjected to solution treatment, and then subjected to pre-stretching treatment and aging treatment in sequence to obtain Al-Zn-Mg-Cu alloy sheet.

[0016] Furthermore, for plates rolled from billets in 6 to 15 passes, the reduction per pass, except for the first two passes, is more than 20 mm.

[0017] Furthermore, the multi-stage homogenization regime consists of holding at 420℃~450℃ for 10~14h, holding at 460℃~495℃ for 18~24h, and holding at 455~470℃ for 6~12h.

[0018] Furthermore, the solution treatment process involves holding at 440℃~460℃ for 2~3 hours and at 470℃~485℃ for 1~2 hours. After the holding period, a spray quenching treatment is performed with a cooling rate ≥10℃ / s and a spray water flow rate ≥10L / s.

[0019] Furthermore, after solution treatment, the rolled sheet is pre-stretched, with a pre-stretch deformation of 3-7%.

[0020] Furthermore, the aging process involves first pre-treating at 100℃~120℃ for 20~32h to form a high-density fine GP region precursor in the alloy matrix, then holding at 165℃~185℃ for 1~6h to melt the grain boundary precipitates, and finally holding at 100℃~120℃ for 20~24h to form a fine, dispersed strengthening phase.

[0021] Furthermore, the thickness of the rolled sheet is 25–152 mm.

[0022] (3) Beneficial effects

[0023] In summary, this invention increases the Zn content in the 7150 alloy and decreases the Cu and Mg content in the 7055 and 7056 alloys, thereby increasing the Zn / Mg ratio and Zn / Cu ratio. This ensures sufficient formation of precipitates while reducing quenching-sensitive elements, which is beneficial for preparing plates with a thickness of 80mm or more. It also strictly controls the impurity content, reduces the embrittlement and corrosion caused by impurity elements such as Fe and Si, compensates for the decrease in toughness and strength caused by the increase in alloying elements, and refines the grains by utilizing the combined effect of Zr and Sc, thereby improving the alloy strength. Attached Figure Description

[0024] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the embodiments of the present invention will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0025] Figure 1 This is a schematic flowchart of a method for preparing a 600MPa grade Al-Zn-Mg-Cu alloy plate according to an embodiment of the present invention. Detailed Implementation

[0026] The embodiments of the present invention will be further described in detail below with reference to the accompanying drawings and examples. The following detailed description of the embodiments and the accompanying drawings are used to illustrate the principles of the present invention by way of example, but should not be used to limit the scope of the present invention. That is, the present invention is not limited to the described embodiments, and any modifications, substitutions and improvements to the parts, components and connection methods are covered without departing from the spirit of the present invention.

[0027] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. This application will now be described in detail with reference to the accompanying drawings and embodiments.

[0028] In the description of this invention, it should be understood that the terms "upper," "lower," "front," "rear," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship commonly used when the product of this invention is in use, or the orientation or positional relationship commonly understood by those skilled in the art. They are only used to facilitate the description of this invention and to simplify the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0029] In the description of this invention, it should also be noted that, unless otherwise explicitly specified and limited, the terms "set" and "install" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a direct connection or an indirect connection through an intermediate medium. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0030] This invention provides a 600MPa grade Al-Zn-Mg-Cu alloy, comprising 7.4–8.5 wt.% Zn, 1.4–2.0 wt.% Mg, 2.0–2.4 wt.% Cu, Zr, Sc, and impurities by mass percentage. The total content of Zr and Sc is 0.04–0.12 wt.%, and the total content of impurities is ≤0.04 wt.%. The Cu / Mg mass percentage ratio is ≥1.2, and the Zn / Mg mass percentage ratio is 4.5–5.1.

[0031] In the above embodiments, the Zn content is increased based on the 7150 alloy, while the Cu and Mg contents are reduced based on the 7055 and 7056 alloys. This increases the Zn / Mg ratio and Zn / Cu ratio, ensuring sufficient precipitate formation while reducing quenching-sensitive elements. This facilitates the preparation of plates thicker than 80mm, strictly controls impurity content, reduces embrittlement and corrosion caused by impurities such as Fe and Si, compensates for the decrease in toughness and strength due to increased alloying elements, and utilizes the combined effect of Zr and Sc to refine grains and improve alloy strength. The strength is increased by 50-100 MPa compared to the widely used 7050 and 7085 alloys, while maintaining comparable toughness and corrosion resistance. This achieves a match between mechanical properties and corrosion resistance, effectively ensuring lightweight aerospace structures, promoting the upgrading of aerospace aluminum alloys, developing corresponding large-scale preparation processes, and advancing the practical application of new aluminum alloys.

[0032] Specifically, when the Sc content is >0.02 wt.%, the total Zr and Sc content is less than 0.08 wt.%; when the Sc content is <0.01 wt.%, the total Zr and Sc content is greater than 0.08 wt.%. The impurities include Cr content ≤0.01 wt.%, Mn content ≤0.01 wt.%, Si content ≤0.02 wt.%, and Fe content ≤0.02 wt.%.

[0033] Figure 1 This is a schematic flowchart of a method for preparing a 600MPa grade Al-Zn-Mg-Cu alloy plate according to an embodiment of the present invention. The method may include the following steps:

[0034] S100: High-purity electrolytic copper, Al-Zr5 master alloy, industrial pure zinc, and high-purity magnesium are added to smelted pure aluminum, mixed evenly, and refined multiple times. After filtration to remove slag, the mixture is cast into ingots.

[0035] Specifically, the proportions of the added elements are consistent with the mass percentages of the elements in the aforementioned ultra-high toughness and high corrosion resistance Al-Zn-Mg-Cu alloy, and will not be elaborated upon here. High-purity aluminum ingots with an aluminum content exceeding 99.9% wt.% and high-purity electrolytic copper (GB / T) can be used. 467-2010), Al-Zr5 master alloy, industrial pure zinc (Zn content exceeding 99.9%), high-purity magnesium (Mg content exceeding 99.92%), refining agent AlTi5B0.2; melting temperature set at 720℃~760℃, first pure Al melting, after complete melting, slag removal, and various alloy ingots and master alloys added, with the assistance of electromagnetic field and ultrasonic vibration stirring technology, after sampling and testing of the composition, it is transferred to a holding furnace and charged with high-purity mixed gas for refining, the refining temperature is 720℃~740℃, after slag removal, the composition is sampled and tested, and a second refining is carried out under high-purity mixed gas, Al-Ti5-B0.2 wire is added, slag is removed by filtration, and then casting is carried out, the casting temperature is set at 730℃~750℃, the casting speed is 40~80mm / min, and the forming thickness is 380~460mm square ingot.

[0036] S200, the ingot is subjected to multi-stage homogenization treatment and multi-pass rolling to obtain rolled plate; the maximum rolling deformation in a single pass is 50mm.

[0037] Specifically, the multi-stage homogenization process involves holding at 420℃~450℃ for 10~14h, at 460℃~495℃ for 18~24h, and at 455~470℃ for 6~12h. The sheet produced by rolling the billet in 6~15 passes has a reduction of over 20mm per pass, except for the first two passes. The thickness of the rolled sheet is 25~152mm.

[0038] S300. The rolled sheet is subjected to solution treatment, and after solution treatment, the rolled sheet is subjected to pre-stretching treatment and aging treatment in sequence to obtain Al-Zn-Mg-Cu alloy sheet.

[0039] Specifically, the solution treatment process involves holding at 440℃~460℃ for 2~3 hours, then at 470℃~485℃ for 1~2 hours. After the holding period, a spray quenching treatment is performed with a cooling rate ≥10℃ / s and a spray water flow rate ≥10L / s. After solution treatment, the rolled sheet undergoes pre-stretching treatment with a pre-stretching deformation of 3~7%. The aging process involves first pre-treating at 100℃~120℃ for 20~32 hours to form a high-density, fine GP region precursor in the alloy matrix, then holding at 165℃~185℃ for 1~6 hours to melt the grain boundary precipitates, and finally holding at 100℃~120℃ for 20~24 hours to form a fine, dispersed strengthening phase. After aging, the sheet is air-cooled to room temperature.

[0040] In the above embodiments, multi-stage homogenization treatment and multi-pass large deformation rolling are adopted to ensure the uniformity of the deformed structure. A three-stage aging process suitable for high alloying aluminum alloys is developed to comprehensively balance intragranular and intergranular precipitates, improve the overall performance, and realize the preparation of 600MPa grade high toughness and high corrosion resistance aluminum alloy plates with a thickness of more than 80mm.

[0041] Example 1

[0042] Step 1: The designed composition is as follows: Zn content 8.2 wt.%, Mg content 1.8 wt.%, Zn / Mg ratio 4.56, Cu content 2.3 wt.%, Cu / Mg ratio 1.28; total Zr+Sc content is 0.05 wt.%, of which Sc content is 0.02 wt.%, and the remainder is Zr; impurity element content is 0.01 wt.%, Mn content is 0.008 wt.%, Si content is 0.01 wt.%, Fe content is 0.01 wt.%, and total impurity content is 0.038 wt.%.

[0043] Step 2: Select high-purity aluminum ingots with an aluminum content exceeding 99.9% wt.%, high-purity electrolytic copper (GB / T467-2010), Al-Zr5 master alloy, industrial-grade zinc (Zn content exceeding 99.9%), and high-purity magnesium (Mg content exceeding 99.92%). Use AlTi5B0.2 as the refining agent. Set the melting temperature to 750℃~760℃. First, melt pure Al. After complete melting, remove the slag and add various alloy ingots and master alloys. With the aid of electromagnetic field and ultrasonic vibration stirring technology, after sampling and testing of the composition, it is transferred to the holding furnace and filled with high-purity mixed gas for refining. The refining temperature is 720℃~730℃. After slag removal, the composition is sampled and tested. After passing the test, it is refined again under high-purity mixed gas. Al-Ti5-B0.2 wire is added, and slag is removed by filtration. Then it is cast. The casting temperature is set at 730℃~740℃, the casting speed is 40~50mm / min, and a square ingot with a forming thickness of 380mm is formed.

[0044] Step 3: The cast billet undergoes multi-stage homogenization treatment, with the homogenization regime being 435℃ for 10 hours, 475℃ for 22 hours, and 460℃ for 8 hours; then it is rolled, and the billet is rolled into a plate with a thickness of 80mm through 8 passes, with a maximum rolling deformation of 44.5mm per pass.

[0045] Step 4: Solution treatment is performed on the rolled sheet. The solution treatment regime is 445℃ for 2 hours and 475℃ for 1 hour. After the solution treatment, spray quenching is performed and the spray water flow rate is ≥10L / s. After solution treatment, the sheet is pre-stretched to eliminate residual stress. The pre-stretch deformation is 3.5%. The pre-stretched sheet is then aged. The aging regime is 110℃ for 24 hours, followed by 185℃ for 1 hour and 121℃ for 20 hours, and then air-cooled to room temperature.

[0046] The 80mm thick Al-Zn-Mg-Cu plate obtained in this embodiment has a tensile strength of over 626MPa and a fracture toughness of 32MPa·m. 1 / 2 The above results indicate that the exfoliation corrosion is rated as EA, demonstrating excellent overall performance.

[0047] Example 2

[0048] In step one, the designed composition is: Zn content 7.9 wt.%, Mg content 1.7 wt.%, and Cu content 2.3 wt.%. The remaining steps are the same as in Example 1.

[0049] The 80mm thick Al-Zn-Mg-Cu plate obtained in this embodiment has a tensile strength of over 613MPa and a fracture toughness of 35MPa·m. 1 / 2 The above-mentioned exfoliation corrosion is rated as EA, indicating good strength, toughness, and corrosion resistance.

[0050] Example 3

[0051] In step one, the designed composition is as follows: 0.008 wt.% of impurity elements Cr, 0.005 wt.% of Mn, 0.006 wt.% of Si, 0.05 wt.% of Fe, and 0.024 wt.% of total impurities. The remaining steps are the same as in Example 1.

[0052] The 80mm thick Al-Zn-Mg-Cu plate obtained in this embodiment has a tensile strength of up to 630MPa and a fracture toughness of 32MPa·m. 1 / 2 The above results indicate that the exfoliation corrosion is rated as EA, demonstrating excellent overall performance.

[0053] Example 4

[0054] The difference from Example 1 is that the billet is subjected to multi-stage homogenization treatment, with the homogenization regime being 440℃ for 10 hours, 485℃ for 18 hours, and 470℃ for 6 hours; then it is rolled, and the billet is rolled into a plate with a thickness of 80mm through 6 passes, with a maximum rolling deformation of 44.5mm per pass. The remaining steps are the same as in Example 1.

[0055] The 80mm thick Al-Zn-Mg-Cu plate obtained in this embodiment has a tensile strength of up to 632MPa and a fracture toughness of 32MPa·m. 1 / 2 The above indicates that the peeling corrosion is classified as EA level.

[0056] Example 5

[0057] The difference from Example 1 is that in step four, the rolled sheet is subjected to solution treatment, with a solution treatment regime of 455℃ for 2 hours and 470℃ for 2 hours. After the solution treatment, a spray quenching treatment is performed, with a spray quenching cooling rate of ≥10L / s. After solution treatment, the sheet is pre-stretched to eliminate residual stress, with a pre-stretch deformation of 5.5%. The pre-stretched sheet is then subjected to aging treatment, with an aging regime of first pre-treatment at 120℃ for 22 hours, then holding at 170℃ for 2 hours, then holding at 115℃ for 24 hours, and finally air-cooled to room temperature. The remaining steps are the same as in Example 1.

[0058] The 80mm thick Al-Zn-Mg-Cu plate obtained in this embodiment has a tensile strength of up to 636MPa and a fracture toughness of 30MPa·m. 1 / 2 The above indicates that the peeling corrosion is classified as EA level.

[0059] Comparative Example 1

[0060] The difference from Example 1 is that the aging process in step four is to first pre-treat at 120°C for 22 hours, then keep warm at 170°C for 0.5 hours, then treat at 120°C for 24 hours, and finally air-cool to room temperature. The remaining steps are the same as in Example 1.

[0061] The 80mm thick Al-Zn-Mg-Cu plate obtained in this embodiment has a tensile strength of over 650MPa and a fracture toughness of K0. IC Less than 25 MPa·m 1 / 2 Its exfoliation corrosion rating is EB, and its strength is significantly higher than that of alloy 7050, but its fracture toughness and exfoliation corrosion rating are both lower than those of alloy 7050.

[0062] The performance comparison of the alloy plates prepared in the above six different embodiments is detailed in Table 1 below:

[0063] Table 1 Performance of Sheets of Different Thicknesses

[0064]

[0065] It should be noted that the various embodiments in this specification are described in a progressive manner, and the same or similar parts between the various embodiments can be referred to mutually. Each embodiment focuses on describing the differences from other embodiments. The present invention is not limited to the specific steps and structures described above and shown in the figures. Furthermore, for the sake of brevity, detailed descriptions of known methods and techniques are omitted here.

[0066] The above are merely embodiments of this application and are not intended to limit the scope of this application. Various modifications and variations can be made to this application by those skilled in the art without departing from the scope of the invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principle of this application should be included within the scope of the claims of this application.

Claims

1. A 600MPa grade Al-Zn-Mg-Cu alloy, characterized in that, It includes 7.4–8.5 wt.% Zn, 1.4–2.0 wt.% Mg, 2.0–2.4 wt.% Cu, Zr, Sc, and impurities by mass percentage, wherein the total content of Zr and Sc is 0.04–0.12 wt.% and the total content of the impurities is ≤0.04 wt.%; wherein the Cu / Mg mass percentage ratio is ≥1.2 and the Zn / Mg mass percentage ratio is 4.5–5.1; When the Sc content is >0.02 wt.%, the total content of Zr and Sc is less than 0.08 wt.%; when the Sc content is <0.01 wt.%, the total content of Zr and Sc is greater than 0.08 wt.%; the content of Cr in the impurities is ≤0.01 wt.%, the content of Mn is ≤0.01 wt.%, the content of Si is ≤0.02 wt.%, and the content of Fe is ≤0.02 wt.%.

2. A method for preparing a plate based on the 600MPa grade Al-Zn-Mg-Cu alloy as described in claim 1, characterized in that, The method includes the following steps: High-purity electrolytic copper, Al-Zr5 master alloy, industrial pure zinc, and high-purity magnesium are added to the smelted pure aluminum and mixed evenly. Various alloy ingots and master alloys are added, and the mixture is refined multiple times. After filtration and slag removal, the ingots are cast. The ingot is subjected to multi-stage homogenization treatment and multi-pass rolling to obtain rolled sheet material. The rolled sheet is subjected to solution treatment, and then subjected to pre-stretching treatment and aging treatment in sequence to obtain Al-Zn-Mg-Cu alloy sheet.

3. The method for preparing the board material according to claim 2, characterized in that, For plates rolled from billets in 6 to 15 passes, the reduction in each pass, except for the first two passes, is more than 20 mm.

4. The method for preparing the sheet material according to claim 2, characterized in that, The multi-stage homogenization process involves holding at 420℃~450℃ for 10~14h, at 460℃~495℃ for 18~24h, and at 455~470℃ for 6~12h.

5. The method for preparing the sheet material according to claim 2, characterized in that, The solution treatment process involves holding the solution at 440℃~460℃ for 2~3 hours and at 470℃~485℃ for 1~2 hours. After the solution treatment is completed, a spray quenching process is applied with a cooling rate ≥10℃ / s and a spray water flow rate ≥10L / s.

6. The method for preparing the sheet material according to claim 2, characterized in that, After solution treatment, the rolled sheet is pre-stretched, with a pre-stretch deformation of 3-7%.

7. The method for preparing the sheet material according to claim 2, characterized in that, The aging process involves first pre-treating at 100℃~120℃ for 20~32h to form a high-density fine GP region precursor in the alloy matrix, then holding at 165℃~185℃ for 1~6h to melt the grain boundary precipitates, and finally holding at 100℃~120℃ for 20~24h to form a fine, dispersed strengthening phase.

8. The method for preparing the sheet material according to claim 2, characterized in that, The thickness of the rolled sheet is 25–152 mm.

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